Keyword:Astragaloside IV, hydrogen peroxide, eNOS uncoupling, NF-κB, NADPH oxidase https://mc06.manuscriptcentral.com/cjpp-pubs production and decrease in intracellular superoxide anion production. Furthermore, pretreatment with AsIV increased endothelial nitric oxide synthase (eNOS) dimer/monomer ratio and its critical cofactor tetrahydrobiopterin (BH 4 ) content, decreased Nox4 protein expression, the most abundant Nox isoform in HUVECs, inhibited translocation of NF-κB p65 subunit into nuclear fraction while enhanced the protein expression of IκB-α, the inhibitor of NF-κB p65, reduced the levels of IL-1β, IL-6 and TNF-α in HUVECs medium, and decreased iNOS protein expression,. These results suggest that AsIV may protect HUVECs from H 2 O 2 induced oxidative stress via inhibiting NADPH oxidase-ROS-NF-κB pathway and eNOS uncoupling.